Fatty acid oxidation (FAO) is required for normal life processes in mammals. Deficiencies of various enzymes that have a role in FAO constitute a family of poorly understood diseases in human patients that range in severity from subclinical manifestations to life threatening disease, including cardiomyopathy, Reye Syndrome (RS)-like disease, and sudden death. The enzyme deficiencies considered prime candidates for important roles in these diseases are; short-chain acyl-CoA dehydrogenase (SCAD), medium-chain acyl-CoA dehydrogenase (MCAD), long-chain acyl-CoA dehydrogenase (LCAD), very long-chain acyl-CoA dehydrogenase (VLCAD), and carnitine palmitoyltransferase I (CPT-1). Additionally, the FAO pathway is important in the pathogenesis of other diseases of energy metabolism, obesity and non-insulin dependent diabetes mellitus (NIDDM). The specific aims of this proposal are to; (i) Complete the production and characterization of MCAD and LCAD deficient mouse models using gene targeting strategies, (ii) Clone and characterize the mouse genes for VLCAD and CPT-1 , and use these genomic segments for gene targeting of their respective loci in mouse embryonic stem (ES) cells to develop mouse models of these enzyme deficiencies as found in children. (iii) Characterize FAO gene expression in mouse mutants of obesity (ob/ob, db/db, AY/+, and fat/fat using the FAO gene probes developed by this project, and (iv) Make selected mouse models with multiple metabolic mutations combining the FAO deficiencies with obesity genes of the mouse mutants characterized in (iii) above. These studies will test the following hypotheses; (i) The acyl- CoA dehydrogenase and CPT-I deficient mouse models will mimic the characteristics of those diseases in children with the same enzyme deficiencies. (ii) FAO gene expression will be markedly reduced in obese mice and this will contribute significantly to the pathogenesis of obesity, and (iii) Obesity combined with FAO deficiency will be especially life threatening because of the expanded substrate base that will be available as free fatty acids (FFAs) through lipolysis during fasting, further overwhelming the extremely compromised stat of the enzyme deficiency. once available, the mouse models produced and characterized will be useful in pursuing many additional specific hypotheses concerning energy metabolism and the interrelationships that exist between its various pathways.